1. Field of the Invention
The present invention relates to a method and device for molding over ski soles by sweeping them with a thermoplastic material.
The development of thermoplastic resins as coating forming the sole or sliding surface of skis has led to the development of machines for repairing or renovating such ski soles, so as to restore a surface condition free from roughness or cracks and give to such coatings the original mechanical characteristics.
2. Description of the Prior Art
Such methods and devices are known for over-molding ski soles, described for example in the patent FR-A-2 391 054. In such a known method, a thermoplastic coating material is continuously fed in solid form into a heating body, shaped as a spreader shoe, the coating material being progressively softened in the heating body and fed in liquid form under the shoe for crushing and spreading over the ski sole during the sweeping or longitudinal translational movement of the shoe on the ski. The device for implementing such a method comprises means for supplying a thermoplastic coating material, a heating body with a spreader shoe shaped so as to receive the coating material in solid form, heat it and progressively soften it, and feed it in liquid form under a distribution and spreading structure intended to be pressed against the ski sole and to be driven in longitudinal translation over said ski sole in a preferential propagation direction. The shoe comprises a projection for preheating the ski sole upstream of the distribution structure.
The material forming ski soles is generally a polyethylene. To provide an over-molding having sufficient properties of clinging to the pre-existing sole, a polyethylene is generally used as thermoplastic coating material in solid, strip, wire or granule form.
For some time, in order to increase the sliding qualities of skis, manufacturers have developed sliding soles made from a very high molecular weight polyethylene. Such ski soles are obtained by sintering and are formed by cutting. The sliding qualities thus obtained are superior to those obtained with lower molecular weight polyethylenes, such as polyethylenes molded when hot at a temperature exceeding the softening point.
It has been noted that when such a sole is over-molded with a very high molecular weight polyethylene using a known molding device, which covers said sole with a molten polyethylene film, a large part of the advantages of the initial very high molecular weight polyethylene sole is lost, and in particular its superior sliding power. Known devices in fact lead to covering the whole of the preexisting sole with a molten polyethylene film, which is then reduced by planing and sanding down.
Attempts have been made to reduce the unfavorable over-molding effects by reducing the final area of the polyethylene deposited by melting. The Applicant has thus attempted to reduce this area by subsequently machining the over-molded sole until the flat parts of very high molecular weight polyethylene appear, leaving the molten polyethylene only in the hollow zones which justified the over-molding. Such attempts have however shown that the result obtained is disappointing, for the sliding qualities of the initial sole are not recovered.
Such a method further leads to a not inconsiderable loss of material, for the known over-molding methods and devices require a thermoplastic material layer of sufficient thickness to be deposited and the greatest part of this thickness must then be removed.